Hi,
Oooh - I live and grew up in Cambridge too and so know it inside out as well; happy to offer some advice. :-))
1Lucie is right; Revolution has cocktail making classes and I can guarantee they do them in Cambridge because I was at one in October last year for a hen night ;-) For about 12-14 of us; it cost £25 I think (sorry can't rememer exact price) and we had the bar upsatirs on the third floor to ourselves from 6:30 - 7:30 on a Saturday night - I'm not sure; but think that might be the last 'slot' on a Saturday evening. Anyway; for that; you get a glass of cheap bubbly each, an intro lesson from the barman and then a cocktail of your choice (from 4), which you make yourself. Once you've finished your cocktail making; they take you down to the main ground floor bar and you get to sit at your reerved table and they bring you plates of food (mini burgers, mini nuggets, mini pizzas etc) - to be honest; it's all really nice food and way too much for everyone to eat! We also had a chocolate fountain with donughts and strawberries to dip; not sure if that was included in the price. Anyway; Id recommend it if you want a loud crazy night; but if you were looking for sophisticated; then Revs is probably not the best place to go 
Mrs Spink to be; I think I know the cocktail place you're talking about - is it the Snug, just down by the Catholic church? They do lovely cocktails; but yep - very pricey.
Also; Salsa - there is a Salsa club called Club Salsa on Station Rd; it's just a 5 minute walk from the Travelodge on Hills Road, which greenleaf mentioned above and is probably your cheapest bet for Cambridge.
oooh I love telling people about this kind of stuff; I knew there must be a reason I keep all this rubbish rattling around in this head of mine - lol
Goodluck vickyc 
PS: Ooh; just though; look at La Raza as somewhere to go too - it's an underground Tapas bar with live music and an area which becomes a dancefloor after 10pm; it's on Rose Crescent by the Market Square.